Weight & Mass Converter

Kilograms, pounds, and the units in between

Weight and mass conversions come up constantly — reading a nutrition label in grams while your kitchen scale shows ounces, checking airline baggage limits in kilograms when you're used to thinking in pounds, or comparing a gym plate loaded in kilograms against a programme written in pounds. This tool covers the everyday range from milligrams (medication dosages, jewellery) up to metric tonnes and US short tons (shipping, construction materials), plus the stone, which remains the everyday unit for body weight across the UK and Ireland.

Mass versus weight, briefly

Strictly speaking, "weight" is a force caused by gravity while "mass" is the amount of matter an object contains — a kilogram of mass weighs slightly less on the Moon than on Earth. In everyday conversations, and in this tool, the terms are used interchangeably because we're all measuring on Earth's surface, and every unit below is defined as a fixed mass regardless of local gravity. That's why a kilogram-to-pound conversion always gives the same answer no matter where you are.

Where the units come from

The kilogram is the SI base unit for mass, currently defined via the Planck constant. The pound (avoirdupois) is legally defined as exactly 0.45359237 kilograms, which is why the 2.20462 lb-per-kg figure you often see is itself a derived approximation, not the original definition. The stone (14 pounds) is a British unit still used in casual conversation about body weight, while the US short ton (2,000 pounds) differs from the UK long ton and the metric tonne (1,000 kg) — mixing these up is a common source of costly errors in shipping and construction quotes, so always confirm which "ton" a contract specifies.

Practical use cases

Home cooks converting a European recipe's grams into US cups-adjacent ounce measurements, parents tracking a baby's weight gain across kilogram-based hospital charts and pound-based family expectations, athletes converting barbell plates between kilogram and pound gyms, and international freight staff double-checking a shipment's declared mass before customs submission all rely on quick, accurate mass conversion. Because the tool works offline once loaded, it's also useful for warehouse or lab environments with limited connectivity.

Getting the most reliable number

For medication or lab work, always keep the full decimal precision shown and cross-check against a second source before acting on the number — this tool is a convenience calculator, not a substitute for a calibrated scale or a pharmacist's guidance. For cooking and fitness, rounding to the nearest gram or tenth of a pound is generally accurate enough. Use the swap button to flip a conversion when you've entered units backwards, and the reference table below the calculator to see how your chosen unit stacks up against the others at a glance.

A quick word on scales and calibration

No converter, including this one, can correct for an inaccurate physical scale. If a kitchen or bathroom scale reads in the "wrong" unit for your needs, converting the number it displays is only as reliable as the scale itself, so it's worth periodically checking a scale against a known reference weight if precision genuinely matters for your task, whether that's a recipe, a shipment, or a training programme.